Oxygen reduction at the surface of glassy carbon electrodes modified with anthraquinone derivatives and dyes

The preparation, electrochemical and catalytic behaviour of glassy carbon electrodes modified by anthra-9,10-quinone, its amino derivatives and dyes were investigated. The stability of the modified electrodes was studied by cyclic voltammetry in acidic and neutral media. The electrocatalytic ability of the modified electrodes for the reduction of dioxygen to hydrogen peroxide was examined by cyclic voltammetry, chronoamperometry and chronocoulometry techniques. The influence of pH on the electrochemical and catalytic behaviour was studied and pH 5.0–8.0 was chosen as the optimum working pH by comparing the shift in oxygen reduction potential. The anthraquinone-adsorbed glassy carbon electrodes possess excellent electrocatalytic abilities for dioxygen reduction with overpotential ranging from 280 to 560 mV lower than that at a plain glassy carbon electrode. Hydrodynamic voltammetric studies were performed to determine the heterogeneous rate constants for the reduction of O₂ at the surface of the modified electrodes, mass specific activity of the anthraquinones used and the apparent diffusion coefficient of O₂ in buffered aqueous O₂-saturated solutions. Studies showed the involvement of two electrons in dioxygen reduction.     

Electrocatalytic activity of hemoglobin in sodium alginate/SiO<Subscript>2</Subscript> nanoparticle/ionic liquid BMIMPF<Subscript>6</Subscript> composite film

A novel biocompatible composite film containing sodium alginate (SA), room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), SiO₂ nanoparticle, and hemoglobin (Hb) was fabricated and covered on the surface of a traditional carbon paste elecrode (CPE). The immobilized Hb on the electrode surface showed good direct electrochemical behaviors, and a pair of quasi-reversible redox peaks of Hb was obtained, which indicated that the direct electron transfer of Hb with the electrode surface had been achieved. The SA/nano-SiO₂/BMIMPF₆/Hb/CPE showed dramatically electrocatalytic activity to the reduction of trichloroacetic acid, hydrogen peroxide (H₂O₂), and oxygen (O₂). The kinetic parameters for the electrocatalytic reactions were evaluated. The composite film showed the potential to the biosensor and biocatalysis.     

Hydrogen peroxide reduction on amalgamated platinum electrodes covered with a monolayer of stearic acid

The reduction of hydrogen peroxide and, for comparison, oxygen on an amalgamated platinum electrode covered with a monolayer of stearic acid is studied by methods of polarization curves and impedance spectroscopy. In contrast with the oxygen reduction, the reduction of dissolved hydrogen peroxide occurs predominantly on the monolayer surface, rather than inside it. This is explained by the difficulty of penetration of the polar molecule of hydrogen peroxide into hydrocarbon environment.     

A Theoretical Study of the Interaction of Hydrogen and Oxygen with Palladium or Gold Adsorbed on Pyridine‐Like Nitrogen‐Doped Graphene

The interaction of H₂ and O₂ molecules in the presence of nitrogen‐doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley–Rideal mechanism and then through a Langmuir–Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.     

酞菁钴及其衍生物修饰电极对分子氧的电催化还原

在玻碳电极上采用吸附法制备了四溴代酞菁钴(CoPcBr₄)、酞菁钴(CoPc)和四-α-(2,2,4-三甲基-3-戊氧基)酞菁钴(CoPc(OC₈H₁₇)₄)修饰电极。利用循环伏安法和线性扫描伏安法研究了修饰电极在酸性介质中对分子氧的电催化还原,比较了不同取代基的酞菁钴对电催化性质的影响。结果表明,它们对分子氧还原均具有良好的电催化活性,其中酞菁钴和四-α-(2,2,4-三甲基-3-戊氧基)酞菁钴对O₂的催化是2电子还原生成H₂O₂,与裸电极相比,O₂的还原峰电位分别向正方向移动了0.33和0.48 V。而四溴代酞菁钴修饰电极在-0.1和-0.7 V附近产生的2个还原峰,说明它催化O₂到H₂O₂的还原以后还可以促进H₂O₂继续还原到H₂O,最终实现O₂的4电子还原。     

Structure-relationships in electrocatalysis: oxygen reduction and hydrogen oxidation reactions on Pt(111) and Pt(100) in solutions containing chloride ions

Kinetics of the oxygen reduction reaction (orr) and the hydrogen evolution–oxidation reactions (her/hor) were studied on the Pt(111) and Pt(100) surfaces in 0.05 M H₂SO₄ containing Cl⁻. The orr is strongly inhibited on the (100) surface modified by adsorbed Cl⁻ (Cl_ad), and it occurs as a 3.5e⁻ reduction via solution phase peroxide formation. In the hydrogen adsorption (H_upd) potential region, the orr is even more inhibited, and corresponds only to a 2 e⁻ reduction at the negative potential limit where the electrode is covered by one monolayer of H_upd and some (unknown) amount of Cl_ad. On the Pt(111)---Cl_ad surface, the orr is inhibited relatively little (in addition to that caused by strong bisulfate anion adsorption on this surface), and the reaction pathway is the same as in Cl⁻ free solution. The kinetics of the hor on Pt(111) are the same in pure solution and in a solution containing Cl⁻, since Cl_ad does not affect platinum sites required for the breaking of the H---H bond. A relatively large inhibition of the hor is observed on the (100) surface, implying that strongly adsorbed Cl_ad is present on the surface even near 0 V.     

Interaction of dioxygen with the platinum Pt19/SnO2/H2 cluster: DFT calculation

The adsorption of the O₂ molecule onto the surface of the Pt₁₉ platinum cluster deposited onto the tin dioxide crystal surface in the presence of dissociated hydrogen molecule has been calculated by the density functional theory method within the generalized gradient approximation (GGA-PBE) with periodic boundary conditions and a projector-augmented plane-wave (PAW) basis set. It has been demonstrated that the oxygen molecule can be adsorbed without a barrier onto the free surface of the Pt₁₉/SnO₂/H₂ cluster to form a superoxy isomer with one Pt-O bond (the energy of elimination of the oxygen molecule is 0.75 eV), which converts almost without a barrier to more stable peroxide isomers with two Pt-O bonds (the energy of elimination of the O₂ molecule is 1.2?1.7 eV). The energy of elimination of the oxygen molecule from the isomers with two-coordinated oxygen positions at the cluster edges is 2.10?2.53 eV. The isomers with mono- and tricoordinated oxygen positions are less energetically favorable than the isomers with two-coordinated oxygen positions. The process of addition of the oxygen molecule to the platinum cluster and elimination of the water molecule formed in the reaction Pt₁₉/SnO₂/H₂ + O₂ → Pt₁₉/SnO₂/O + H₂O is energetically favorable by 1.6 eV.     

Simple Electrodeposition of Dendritic Pd Without Supporting Electrolyte and Its Electrocatalytic Activity Toward Oxygen Reduction and H2O2 Sensing

Metallic palladium (Pd) electrocatalysts for oxygen reduction and hydrogen peroxide (H₂O₂) oxidation/reduction are prepared via electroplating on a gold metal substrate from dilute (5 to 50 mM) aqueous K₂PdCl₄ solution. The best Pd catalyst layer possessing dendritic nanostructures is formed on the Au substrate surface from 50 mM Pd precursor solution (denoted as Pd‐50) without any additional salt, acid or Pd templating chemical species. The Pd‐50 consisted of nanostructured dendrites of polycrystalline Pd metal and micropores within the dendrites which provide high catalyst surface area and further facilitate reactant mass transport to the catalyst surface. The electrocatalytic activity of Pd‐50 proved to be better than that of a commercial Pt (Pt/C) in terms of lower overpotential for the onset and half‐wave potentials and a greater number of electrons (n) transferred. Furthermore, amperometric i–t curves of Pd‐50 for H₂O₂ electrochemical reaction show high sensitivities (822.2 and ?851.9 µA mM^?1 cm^?2) and low detection limits (1.1 and 7.91 µM) based on H₂O₂ oxidation H₂O₂ reduction, respectively, along with a fast response (<1 s).     

Sensing and catalytic decomposition of hydrogen peroxide by silicon carbide nanotubes: A DFT study

In this study, by carrying out detailed density functional theory calculations, we investigate the adsorption and stepwise decomposition of hydrogen peroxide (H₂O₂) over (6,0) and (7,0) zigzag silicon carbide nanotubes (SiCNTs). The results indicate that the H₂O₂ can be adsorbed on the exterior surface of the SiCNTs with noticeable adsorption energies and charge transfers. To gain insight into the catalytic activity of the surface, the interaction between the H₂O₂ and SiCNT is analyzed by detailed electronic analysis such as adsorption energy, charge density difference and activation barrier. The decomposition of H₂O₂ into O₂ and H₂ species can be viewed as the kinetically preferred reaction pathway for dehydrogenation of hydrogen peroxide over SiCNTs. There is also a curvature effect on the dehydrogenation kinetics of hydrogen peroxide, that small diameter SiCNTs with large curvature would be beneficial for decomposition of H₂O₂. © 2015 Wiley Periodicals, Inc.     

Simultaneous Detection of Peracetic Acid and Hydrogen Peroxide by Amperometry at Pt and Au Electrodes

Based on preliminary voltammetric investigations at both Pt and Au electrodes in aqueous solutions buffered at different pH values in the range 0–10, two possible profitable triple‐pulse amperometric approaches were developed for determining simultaneously peroxyacetic acid (PAA) and hydrogen peroxide present in the same samples. At both surfaces a pulsed waveform applied at rotating‐disc electrodes was adopted to take advantage on one hand of the optimized signal reproducibility achieved by this potential multistep antifouling approach and on the other hand of the constant thickness of the diffusion layer, which is necessary when the recording of time‐independent currents is desired. At a rotating‐disc Pt electrode an anodic selective signal was indeed recorded for H₂O₂ alone, while PAA contents could be inferred only from the difference of convenient signals, since at all pHs explored its sole cathodic reaction could be observed at potentials coincident with those proper for the reduction of H₂O₂ too. The same pulse approach at Au electrodes instead provided totally independent signals for the two analytes considered, thus proving to be suitable for their independent detection. In fact, H₂O₂ alone undergoes anodic oxidation also at this surface, while the reduction of PAA occurs at potentials less cathodic than those required for H₂O₂. At both electrodes, the best results turned out to be achieved at pH 0 in terms of both precision (±2–4%) and detection limits (0.2–0.3 mM), as well as of linear range which extended for about three orders of magnitude. The kinetics of the equilibrium involving the generation of H₂O₂ from the reaction of PAA with water was also evaluated, since it was suspected of making unreliable the proposed amperometric approaches.     

Effect of hydrogen gas impurities on the hydrogen dissociation on iron surface

A small addition of oxygen to hydrogen gas is known to mitigate the hydrogen embrittlement (HE) of steels. As atomic hydrogen dissolution in steels is responsible for embrittlement, catalysis of molecular hydrogen dissociation by the steel surface is an essential step in the embrittlement process. The most probable role of oxygen in mitigating HE is to inhibit the reactions between molecular hydrogen and the steel surface. To elucidate the mechanism of such surface reaction of hydrogen with the steel in the presence of oxygen, hydrogen, and oxygen adsorption, dissociation, and coadsorption on the Fe(100) surface were investigated using density functional theory. The results show that traces of O₂ would successfully compete with H₂ for surface adsorption sites due to the grater attractive force acting on the O₂ molecule compared to H₂. The H₂ dissociation would be hindered on iron surfaces with predissociated oxygen. Prompted by the notable results for H₂ + O₂, other practical systems were considered, that is, H₂ + CO and CH₄. Calculations were performed for the CO chemisorption and H₂ dissociation on iron surface with predissociated CO, as well as, CH₄ surface dissociation. The results indicate that CO inhibition of H₂ dissociation proceeds via similar mechanism to O₂ induced inhibition, whereas CH₄ traces in the H₂ gas have no effect on H₂ dissociation. © 2014 Wiley Periodicals, Inc.     

Electrocatalytic Reduction of Oxygen at Anthraquinonedisulfonate/Polypyrrole Composite Film Modified Electrodes and Its Application to the Electrochemical Oxidation of Azo Dye

We report here the electrocatalytic reduction of oxygen on thin anthraquindisulfonate (AQDS)/poplypyrrole (PPy) composite film modified electrodes and its application to the electrooxidation of azo dye‐amaranth. The polymer‐coated cathode exhibited good electrocatalytic activity towards oxygen reduction reaction (ORR), and allowed the formation of strong oxidant hydroxyl radical (^.OH) in the medium via Electro‐Fenton's reaction between cathodically generated H₂O₂ and added or regenerated Fe²⁺. The electrochemical behaviors of ORR in various pH solutions were described using cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometric (CA) techniques. The effect of solution pH on amaranth mineralization by the Fe²⁺/H₂O₂ and Fe³⁺/H₂O₂ electrooxidation systems was studied. In addition, the long‐term electrocatalytic activity and stability of the AQDS/PPy composite film during multiple experimental runs were also examined electrochemically.     

The effect of doping of the ultradispersed nickel powder by pyrocarbon on oxygen adsorption and Oads + CO reaction

Oxygen adsorption and chemisorption and the kinetics of interaction between adsorbed oxygen and CO on nickel ultradispersed powder (average size of particles, 20 nm) are studied. The ultradispersed nickel powder was dosed by the products of pyrolysis of chemisorbed ethylene (pyrocarbon) in the amount of 0.1–1.6 of a monolayer. The spectra of ferromagnetic resonance of the ultradispersed nickel powder before and after ethylene adsorption and pyrolysis and after adsorption and chemisorption of oxygen and its reduction by hydrogen are recorded. The magnetization of ultradispersed nickel powder increases upon dosing the surface with ethylene (C₂H_4ads) and pyrocarbon in the amount of 0.5 of a monolayer. Pyrocarbon inhibits the O_ads + CO reaction. The reaction orders with respect to O_ads and CO and the experimental activation energy change. The effects of small (less than a monolayer) and large (more than a monolayer) amounts of the modifying agent are different.     

Hydrogen redox reactions in 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide on platinum single crystal electrodes

Hydrogen oxidation and the subsequent proton reduction are studied on platinum single crystal electrodes in purified 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid. The hydrogen redox reaction shows some dependence of the surface orientation. The highest reversibility is observed with Pt(111) whereas the reaction in electrodes with {100} sites is less reversible and with a slow kinetics. Adsorption states are observed in the presence of hydrogen along with the main oxidation reaction. Also, it is possible to detect protons after oxidation of water and H₂O₂.     

Direct Detection of the Superoxide Anion as a Stable Intermediate in the Electroreduction of Oxygen in a Non‐Aqueous Electrolyte Containing Phenol as a Proton Source

The non‐aqueous Li–air (O₂) battery has attracted intensive interest because it can potentially store far more energy than today′s batteries. Presently Li–O₂ batteries suffer from parasitic reactions owing to impurities, found in almost all non‐aqueous electrolytes. Impurities include residual protons and protic compounds that can react with oxygen species, such as the superoxide (O₂^?), a reactive, one‐electron reduction product of oxygen. To avoid the parasitic reactions, it is crucial to have a fundamental understanding of the conditions under which reactive oxygen species are generated in non‐aqueous electrolytes. Herein we report an in situ spectroscopic study of oxygen reduction on gold in a dimethyl sulfoxide electrolyte containing phenol as a proton source. It is shown directly that O₂^?, not HO₂, is the first stable intermediate during the oxygen reduction process to hydrogen peroxide. The unusual stability of O₂^? is explained using density functional theory (DFT) calculations.     

Silver nanoparticle assemblies supported on glassy-carbon electrodes for the electro-analytical detection of hydrogen peroxide

Electrochemical detection of hydrogen peroxide using an edge-plane pyrolytic-graphite electrode (EPPG), a glassy carbon (GC) electrode, and a silver nanoparticle-modified GC electrode is reported. It is shown, in phosphate buffer (0.05 mol L^–1, pH 7.4), that hydrogen peroxide cannot be detected directly on either the EPPG or GC electrodes. However, reduction can be facilitated by modification of the glassy-carbon surface with nanosized silver assemblies. The optimum conditions for modification of the GC electrode with silver nanoparticles were found to be deposition for 1 min at –0.5 V vs. Ag from 5 mmol L^–1 AgNO₃/0.1 mol L^–1 TBAP/MeCN, followed by stripping for 2 min at +0.5 V vs. Ag in the same solution. A wave, due to the reduction of hydrogen peroxide on the silver nanoparticles is observed at –0.68 V vs. SCE. The limit of detection for this modified nanosilver electrode was 2.0×10^–6 mol L^–1 for hydrogen peroxide in phosphate buffer (0.05 mol L^–1, pH 7.4) with a sensitivity which is five times higher than that observed at a silver macro-electrode. Also observed is a shoulder on the voltammetric wave corresponding to the reduction of oxygen, which is produced by silver-catalysed chemical decomposition of hydrogen peroxide to water and oxygen then oxygen reduction at the surface of the glassy-carbon electrode.     

Electrosynthesis of hydrogen peroxide in solutions of salts that form molecular addition products (peroxo solvates) with it

The possibility of electrosynthesis of hydrogen peroxide in the electroreduction of oxygen in a gas-diffusion electrode in solutions of salts that form the molecular addition products (peroxo solvates) with H₂O₂ was studied. In KF and potassium and sodium phosphate solutions, H₂O₂ was obtained at concentrations of 2.3–3.6 M at current densities of 0.1–0.15 A/cm² and current efficiencies of 75–92%. The resulting solutions were concentrated to 11–27 M to give solid peroxo solvates with high hydrogen peroxide contents (22–50%). These results demonstrate that the application of gas-diffusion electrodes for electrosynthesis of inorganic products can be significantly expanded.     

On the mechanism of H2O2 reduction at Prussian Blue modified electrodes

Prussian Blue deposited on the electrode surface under certain conditions is known to be a selective electrocatalyst of hydrogen peroxide (H₂O₂) reduction in the presence of O₂. The electrocatalyst was stabilized at cathodic potentials preventing its loss from the electrode surface. Hydrodynamic voltammograms of H₂O₂ reduction indicated the transfer of two electrons per catalytic cycle. The operational stability of Prussian Blue in H₂O₂ reduction was highly dependent on the buffer capacity of the supporting electrolyte. Since Prussian Blue is known to be dissolved in alkaline solution, it was confirmed that in neutral aqueous solutions the product of H₂O₂ electrocatalytic reduction is OH⁻.     

Electrocatalysis of oxygen reduction on glassy carbon electrodes modified with anthraquinone moieties

Anthraquinone groups were electrochemically grafted to glassy carbon (GC) electrodes via methylene linker to study the oxygen reduction reaction (ORR) in alkaline medium. Two different anthraquinone derivatives, 2-bromomethyl-anthraquinone or 2-chloromethyl-anthraquinone, were used to modify the GC electrode surface. Several modification conditions encompassing potential cycling and electrolysis at a fixed potential were employed in order to vary the surface concentration of MAQ groups (Γ _MAQ) and to study the dependence of the O₂ reduction behaviour on electrografting procedure. Cyclic voltammetry confirmed the presence of anthraquinone moieties attached to the GC electrode and Γ _MAQ varied in the range of (0.5–2.4)?×?10^?10 mol cm^?2. Oxygen reduction was studied on MAQ-modified GC electrodes of various surface coverage using the rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods. The RDE and RRDE results of O₂ reduction reveal that GC/MAQ electrodes show rather similar electrocatalytic behaviour towards the ORR yielding hydrogen peroxide as the final product.     

Synthesis of Hydrogen Peroxide Using Dielectric Barrier Discharge Associated with Fibrous Materials

A new synthesis pathway toward hydrogen peroxide has been investigated using non-thermal plasma. This work is aimed at studying the activation of oxygen/hydrogen mixtures by a cylindrical dielectric barrier discharge. An experimental device has been especially developed for this application, it mainly differs from other cylindrical discharges in that the liquid ground electrode, and subsequently the reactor, can be regulated in temperature. The formation of hydrogen peroxide is reported (1) in a gas phase discharge and (2) in surface discharge. The gas phase discharge, characterized by an empty discharge gap, lead to a low activation of O₂ into O₂/H₂ mixtures and poor selectivity toward H₂O₂. The modification of the discharge into a surface discharge, by introducing in the gap fibrous materials, considerably improves the efficiency of the process. The influence of the temperature on H₂O₂ formation is discussed and correlated to the formation of a water layer on fibre surface. This layer appears to be a crucial point into H₂O₂ plasma synthesis. The presence of TiO₂ on the fibre surface is reported as improving the stabilisation of hydrogen peroxide. The formation of a complex between H₂O₂ and TiO₂ is suggested and discussed. The formation of H₂O₂ in the gas phase or in the aqueous condensed phase is finally discussed. The investigation of the influence of the reactant gas composition and the presence or not of water, lead to the conclusion that (1) both H₂ and O₂ are required to achieve the synthesis reaction; (2) H₂O₂ is formed in the gas phase and then solubilised and/or stabilised in the water layer. A global reaction pathway is finally proposed to summarize the synthesis reaction.